test(ai): baseline 4 local CPU models + fix prompt-fairness bug

Capture native-harness benchmark baselines for qwen2.5 0.5b/1.5b/3b and
qwen2.5-coder:7b (all probed tool-capable; deepseek-r1 and NL2SH reject the
tools field). All cluster at 1-2/12 with high variance; the 7B buys no
pass-rate gain at ~3x latency, so qwen2.5:3b stays the default. The single
biggest score sink across every model is bare tool-call-as-text leaks — a
harness parse gap, the clear next improvement.

Also drop "in your home directory" from the shell prompts: it made literal-
minded models create a home/ subdir (/root/home/a/b/c/...) or use ~/, which
the benchmark itself surfaced. Findings doc + bench README carry the model
comparison table and recommendations (llama3.2:3b / llama3.1:8b for a non-qwen
data point).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bench/README.md

@@ -66,3 +66,20 @@ A PASS/FAIL table with per-task latency, plus a JSON record under
 `bench/results/` (gitignored — these are runtime artifacts). Commit a curated
 baseline explicitly (e.g. `--out bench/results/baseline-<model>.json` then
 `git add -f`) when you want one tracked for comparison.
+
+## Tracked baselines (2026-06-10, CPU-only, shared room)
+
+| model | size | PASS | avg/med s |
+|---|---|---|---|
+| qwen2.5:0.5b | 397 MB | 1/12 | 55 / 49 |
+| qwen2.5-coder:1.5b | 986 MB | 1/12 | 67 / 53 |
+| **qwen2.5:3b** | 1.9 GB | 1/12 | 51 / 46 |
+| qwen2.5-coder:7b | 4.7 GB | 2/12 | 141 / 106 |
+
+All cluster at 1–2/12 with high run-to-run variance — treat as a *relative*
+regression yardstick, not an absolute grade. The 7B buys no pass-rate gain at
+~3× latency; **qwen2.5:3b stays the default**. The biggest score sink across
+every model is bare tool-call-as-text leaks (a harness parse gap, not model
+capability) — see `docs/findings-native-harness-2026-06-10.md`. Only
+qwen2.5(-coder) sizes 0.5b–7b are usable here; `deepseek-r1` and
+`westenfelder/NL2SH` reject Ollama's `tools` field.